Electric low-voltage fuse

ABSTRACT

A low-voltage fuse, and in particular a low-voltage fuse of the polyphase variety, has a specific array of fusible currentcarrying means arranged between juxtaposed surfaces of a pair of spaced terminal bars. These surfaces are provided with grooves extending in a direction longitudinally of said pair of terminal bars. The aforementioned array of current-carrying means is formed by a plurality of stampings of silver or copper, each including a pair of spaced terminal strips and each further including a plurality of terminal-strip-interconnecting fusible elements in ribbon form. The length of each of said fusible elements of said plurality of stampings exceeds the spacing between said pair of terminal bars. The aforementioned stampings are inserted with the terminal strips thereof into the grooves of said pair of terminal bars in such a way that all constituent fusible elements of each of said plurality of stampings are out of registry with any of the constituent fusible elements of any other of said plurality of stampings. The constituent fusible elements of said stampings are further bent alternately in opposite directions away from the median plane of said pair of terminal bars, thus assuming a substantially C-shaped configuration.

United States Patent Belcher et a1. 1451 Oct. 10, 1972 [541 ELECTRIC LOW-VOLTAGE FUSE [57] ABSTRACT [72] Inventors: Richard A. Belcher, Hampton Falls; A low-voltage fuse, and in particular a low-voltage Frederick J. Kozacka, South Hampfuse of the polyphase variety, has a specific array of ton, both of NH. fusible current-carrying means arranged between juxml cw urypo a direction longitudinally of said pair of terminal bars. [22] Filed: Aug. 24, 1971 The aforementioned array of current-carrying means is formed by a plurality of stampings of silver or [21] Appl l74455 copper, each including a pair of spaced terminal strips and each further including a plurality of terminal- [52] US. Cl. ..337/16l, 337/231, 337/252 strip-interconnecting fusible elements in ribbon form. [51] Int. C1,...H01h 85/08, 1-[01h 85/ 12, H01}; 85/60 The length of each of said fusible elements of said plu- [58] Field of Search ..337/158, 159, 160, 161, 228, j y of mp g exceeds the p n between said 337/229, 231, 232, 233, 244, 246, 251, 252, palnof terminal bars. Theafbrementroned stampmgs 293 are inserted with the term nal stnps thereof mto the grooves of said pair of terminal bars in such a way that [56] References Cited all constituent fusible elements of each of said plurality of stampmgs are out of registry with any of the con- UNITED STATES PATENTS stituent fusible elements of any other of said plurality of stampings. The constituent fusible elements of said 3,593,251 7/1971 W 1lson ..337/16l U X stampmgs are further bent alternately in opposite 33l9027 5,1967 Hitchcock "337/244 UX directions away from the median plane of said pair of 3,132,223 5/1964 Jacobs, Jr. ..337/161 x terminal bars thus assuming a Substantially Gshaped 2,918,551 12/1959 Kozolka ..337/244 configuration 2,202,719 5/1940 Schmidt ..337/244 1?. C m 8 rewi sf s s Primary Examiner-Bernard A. Gilheany Assistant Examiner-Dewitt M. Morgan Attorney-Erwin Salzer 21 f as I f 5 l 5 8 I 4 a l IO 9- 1 l PATENTEDUBI 10 I972 SHEET 1 OF 3 \IA mm Y E Z R O 0 W K T T EAJ V KM W W W MT mw PATENTEDHBH 3.697.916

saw 2 OF 3 FIG. 5.

|NVENTORS= RICHARD A.BELCHER, FQEDERQCK J. KOZACKA, BY AMA/m ATTORNEY PATENTEDBBT 101912 3.697.916

SHEET 3 BF 3 INVENTORS= RICHARD ABELCHER, FREDERICK J.KOZACKA, BY NAM W A TORNEY ELECTRIC LOW-VOLTAGE FUSE BACKGROUND OF THE INVENTION The principal object of this invention is to provide fuses, and more particularly polyphase fuses, of reduced size which lend themselves for back-up protection of a new generation of molded case circuit breakers of reduced size. To be more specific, this invention provides means allowing to reduce the spacing between the terminal bars of a polyphase fuse to about 1 inch for a wide band of current ratings and a voltage rating of 600 volt.

Comparable prior art polyphase fuses require larger housings than polyphase fuses according to the present invention, and in particular require spacings between the terminal bars thereof about percent larger than polyphase fuses embodying this invention.

The present invention is an outgrowth and further development of the kind of polyphase fuses disclosed and claimed in the copending patent applications of Frederick J. Kozacka, filed Dec.8,1970, Ser. No. 96,110 for COMPACT POLYPHASE FUSE and of Kenneth W. Swain, filed Dec.l5,l970, Ser.No. 98,422 for POLYPHASE FUSE WITH BLOWN FUSE IN- DICATOR IN EACH PHASE now abandoned in favor of continuation application Ser. No. 193,596 filed Oct. 28, I971. The present invention adapts the structures shown in the two aforementioned copending patent applications to very high current ratings.

SUMMARY OF THE INVENTION Electric low-voltage fuses embodying this invention include a housing of electric insulating material defining an elongated i.e. substantially closed at one side of said housing and open at the opposite side thereof. A pair of terminal bars is arranged inside of and at opposite sides of said cavity and has ends projecting away from said housing. Said pair of terminal bars is arranged in abutting relation to opposite walls of said housing bounding said cavity and is affixed to said opposite walls. Said housing is the only means spacing said pair of terminal bars, i.e. any additional insulating spacing means for said pair of terminal bars engaging said pair of terminal bars is excluded from said cavity. Said pair of terminal bars has a plurality of grooves in the juxtaposed surfaces thereof extending in a direction longitudinally of said pair of terminal bars. The aforementioned cavity is filled with a pulverulent arcquenching filler. A cover of insulating material is attached to the housing and closes the open side of said cavity. The fuse further includes a plurality of stampings of a current limiting metal, i.e., silver or copper. Each of said stampings includes a pair of spaced terminal strips, and a plurality of terminal-stripinterconnecting fusible elements in ribbon form. Each of said plurality of fusible elements has a predetermined length exceeding the spacing between said pair of terminal bars. Said plurality of stampings is inserted with said pair of terminal strips thereof into said plurality of grooves in said pair of terminal bars and conductively connected to said pair of terminal bars. The constituent fusible elements of said plurality of stampings are arranged substantially out of registry, as seen in a direction transversely to said pair of terminal bars. The constituent fusible elements of said plurality of stampings further have convex shapes and are bent away from the median plane of said pair of terminal bars. Fusible elements contiguous in a direction longitudinally of said pair of terminal bars are bent alternately in opposite directions.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a rear elevation of a polyphase or threephase current-limiting fuse embodying the present invention;

FIG. 2 is a side elevation of the structure of FIG. I drawn on the same scale as FIG. 1;

FIG. 3 is aside elevation of the structure of FIG. 1 and is drawn on a plane at right angles to the plane on which FIG. 1 is drawn;

FIG. 4 is mainly a section along 4-4 of FIG. 1;

FIG. 5 is mainly a section along 5-5 of FIG. 1, some parts, however, being shown in elevation rather than in section;

FIG. 6 is a front elevation of a detail of the structure of FIG. 1 drawn on a larger scale than FIG. I;

FIG. 7 is a section along 7-7 of FIG. 6; and

FIG. 8 shows in side elevation the several constituent stampings of the array of stampings shown in FIGS. 6 and 7.

DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION In the drawings reference numeral 1 has been applied to indicate a housing of a synthetic resin, or other electric insulating material. Housing 1 is closed by a cover 2 of an electric insulating material which is also preferably a synthetic resin. The cover 2 of housing I is provided with circular apertures 13 receiving closing plugs 14 (FIGS. 4 and 5). Reference character 5 has been applied to indicate three pairs of terminal bars made preferably of electrolytic copper. Each terminal bar includes two sections of which one projects into housing 1 and the other projects away from housing 1. Housing 1 defines three elongated cavities 6 separated by partitions 7 as best shown in FIG. 4. Each cavity 6 is substantially closed at one side and open at the opposite side of housing I. To be more specific, each cavity is substantially closed at the side of housing I where the indicator pins 4 are arranged, and open at the side of housing 1 where the latter is covered by cover 2. As best shown in FIG. 5 housing 1 defines recesses 7' engaged by the ends of terminal bars 5 projecting into cavities 6, and terminal bars 5 are provided with small projections 8 adjacent their bend of degrees cooperatively engaging the outer surface of housing 1. Recesses 7 and projections 8 are, in effect, fastener means for affixing terminal bars 5 to housing I. The portions of terminal bars 5 situated inside of cavities 6 are arranged in abutting relation to opposite walls of housing 1 forming cavities 6. Housing 1 is the only means for positioning and for spacing terminal bars 5. To be more specific, any additional spacing means of insulating material for terminal bars 5 engaging juztaposed terminal bars 5 in each cavity 6 are dispensed with. Since cavities 6 are unencumbered by insulating terminal-bar-spacing means, the entire volume of each of cavities 6 is available for current-carrying ribbon fuse link means and for pulverulent arc-quenching filler, as will be explained below more in detail. The exclusion of additional insulating spacing means for each pair of terminal bars reduces significantly the cost of manufacture and increases the interrupting ability of the arc-quenching filler, thus minimizing the required ,spacing between juxtaposed terminal bars 5, and concomitantly minimizing the bulk of the entire fuse structure. .Iuxtaposed surfaces of terminal bars 5 are provided with a plurality of grooves 9 extending in a direction longitudinally of terminal bars 5, i.e. longitudinally of that portion of terminal bars 5 arranged in cavities 6. This is best shown in FIGS. 5 and 6. As shown in FIG. 6 each terminal bar 5 is provided with four grooves 9 the length of which is substantially equal to the length of the sections of terminal bars 5 projecting into cavities 5. The number of grooves is preferably four if it is intended to maximize the current-carrying capacity of the fuse structure, but may be smaller if it is not necessary to maximize current-carrying capacity. A pulverulent arc-quenching filler 10 such as quartz sand is arranged inside of each cavity 6. In FIGS. 4 and 5 the body of arc-quenching filler 10 is broken away to better show the other parts situated within cavities 6.

Housing 1 defines three substantially identical cavities of which each is provided with identical currentcarrying and current-interrupting means. FIGS. 4 and 5 show one of the three cavities and all the parts within, or operatively related to, that cavity. Since all cavities 6 are identical and house identical parts, illustration and description of but one of the three cavities 6 of housing 1 is sufficient to disclose the entire polyphase fuse structure. In FIG. 4 one cavity and its contents have been fully shown, and an adjacent cavity has also been indicated. The latter cavity is, however, only shown in part and its contents has been entirely deleted.

The cover 2 of electric insulating material, preferably a synthetic resin, has three plugged apertures 13 allowing, when unplugged, to fill each of the three cavities 6 with a pulverulent arc-quenchingfiller 10. In FIGS. 1,4 and 5 reference character 14 has been applied to indicate plugs for closing apertures 13 after casing l, or its cavities 6, respectively, have been filled with a pulverulent arc-quenching filler. Plugs 14 are preferably castings of an epoxy resin. There is an interface 15 between housing 1 and cover 2. A sealing layer of cured silicon resin paste is arranged at the aforementioned interface to firmly seal cover 2 to housing 1. Housing 1 and cover 2 are further tied together by a plurality of screw-threaded studs and screw-nuts to which reference character 16 has been applied.

Housing 1 is provided with phase-separating barriers 17 forming an integral part thereof, and cover 2 is provided with similar phase-separating barriers 18 forming an integral part thereof.

Cover 2 defines three cavities 12 of which each forms an extension of one of the cavities 6 defined by housing 1. Thus housing 1 and cover 2 define jointly composite cavities 6,12 of increased size, i.e. each composite cavity 6,12 is larger than one of the housing cavities 6 as such. The bodies of pulverulent filler 10 extend into cavities 12 and fill the latter. The bottom of cavities 12 is concave, or converging toward apertures 13. As a result, cast plugs 14 form rivet-head-like projections having a larger diameter than the diameter of circular apertures 13, and overlapping the concave or converging bottom of cavities 12. Therefore, plugs 14 are mechanically interlocked with cover 2, and there is no danger whatever that they might be pushed out of apertures 13 under the action of high pressures prevailing in composite cavities 6,12 incident to interruption of major fault currents, or short-circuit currents.

Grooves 9 in terminal bars 5 receive a plurality of identical stampings shown in FIGS. 7 and 8. To be more specific, in the embodiment of the invention the four grooves 9 in each terminal bar 5 receive four stampings A,B,C,D. Each stamping A,B,C,D is made of a current-limiting metal. The term current-limiting metal is used in this context as a generic term encompassing silver and copper. Each stamping A,B,C,D includes a pair of spaced parallel terminal strips 19 and a plurality of terminal-strip-interconnecting fusible elements 20,21,22 in ribbon form. In FIG. 6 reference character S has been applied to indicate the spacing between terminal bars 5, i.e. the spacing between the sections of terminal bars 5 which project into cavities 6. Fusible elements 20,21,22 have a predetermined length which exceeds the spacing S of terminal bars 5. Stampings A,B,C,D are inserted with the terminal strip 19 thereof into grooves 9 and conductively connected or soldered to terminal bars 5. The constituent fusible elements 20,21, 22 of stamping A,B,C,D are arranged out of registry as seen in a direction transversely to the portions of terminal bars 5 projecting into cavities 6. This direction has been indicated in FIG. 6 by the arrow R. Being out of registry is intended to denote the fact that none of the fusible elements 20,21,22 of any stamping A,B,C,D overlaps a fusible element 20,21,22 of any other stamping A,B,C,D when the array of stampings A,B,C,D is viewed in the direction of the arrow R. This is clearly shown in FIG. 5. The fusible elements 20,21,22 of stampings A,B,C,D are convex in shape, as best shown in FIG. 6, and bent away from the median plane of terminal bars 5. This plane has been indicated in FIGS. 6 and 7 by the dash-and-dot lines M. Fusible elements 20,21,22 contiguous in a direction longitudinally of terminal bars 5 are bent alternately in opposite directions. This may be readily understood when denoting each fusible element by the reference letter of the stamping to which it pertains. Thus A 20 is a particular fusible element 20 pertaining to stamping A, and D 22 is a particular fusible element pertaining to stamping D. As apparent from FIGS. 7 and 8 the sequence of fusible elements in a direction longitudinally of terminal bars 5 is as follows: A 20; C 20; B 20; D 20; A 21; C 21; B 21; D 21; A 22; C 22', B 22; D 22. A 20 is bent to the right away from plane M; C 20 is bent to the left away from plane M; B 20 is bent to the right away from plane M; D 20 is bent to the left away from plane M; A 21 is bent to the right away from plane M; etc.

Numerous tests have shown that the above geometry of stampings A,B,C,D is of crucial importance to minimize the spacing S, and at the same time to maximize the current-carrying ability and interrupting ability of the fuse structure.

As best shown in FIGS, the portions of terminal bars 5 projecting into cavity 6 converge slightly from the open side of cavity 6 toward the closed side thereof. In other words, the angle enclosed between both sections of terminal bars 5 may slightly exceed e.g. be 91. The fusible elements 20,21,22 of stampings A,B,C,D are of equal length and the radii of curvature of fusible elements 20,21,22 decrease progressively from the open side toward the closed side of cavity 6. In other words, the smaller the spacing between terminal bars 5 on account of their convergence, the smaller the radius of curvature (or the larger the curvature) of the particular fusible element 20,21,22 positioned between terminal bars 5. This geometry is of particular importance when it is desired to provide the fuse structure with blown fuse indicators.

FIGS. 4 and 5 show blown fuse indicator of the character disclosed and claimed in the copending patent application of Kenneth W. Swain, filed Dec. 15,1970, Ser.No. 98,422 for POLYPHASE FUSE WITH BLOWN FUSE INDICATOR IN EACH PHASE now abandoned in favor of continuation application Ser. No. 193,596 filed Oct. 28, 1971. Thewall of housing 1 is provided with a bell-shaped projection 23 extending into cavity 6. Projection 23 defines a space separate from cavity 6 which houses a conventional blown fuse indicator 24 including the spring-biased indicator pin 3. The latter is normally restrained by a substantially V-shaped restraining wire 25 of steel of which one end is conductively connected to one of terminal bars 5, and the other end is conductively connected to the other of terminal bars 5. The converging center portion of restraining wire 25 is affixed to spring-biased indicator pin 4 and normally restrains the latter in the position shown in FIGS. 4 and 5. Restraining wire 25 is normally shunted by fusible elements 20,21,22 and, therefore, normally not current-carrying. Upon interruption of the current paths provided by fusible elements 20,21,22 a significant voltage appears across terminal bars 5, causing wire 25 to carry current and to fuse, thus releasing indicator pin or pins 4. The latter are then propelled by spring action forwardly, thus indicating that one or more phase units of the fuse have blown.

In a fuse structure of the general character under consideration the presence of a blown fuse indicator is a serious potential danger. This is due to the fact that terminal bars 5 and stampings A,B,C,D form a loop resulting in an intense electrodynamic action upon the products of arcing and the arcs proper which take the place of fusible elements 20,21,22 upon blowing of the fuse. The hot products of arcing and the arcs tend to be swept by electrodynamic action toward the blown fuse indicator, destroying the latter and causing the entire fuse structure to fail. This tendency is greatly increased if the spacing S between the terminal bars 5 is reduced to a smaller magnitude than that found necessary in comparable prior art fuses. To minimize the danger of destruction of the blown fuse indicator the fusible elements 20,21,22 are kept away from the latter as much as possible and the fusible elements 20,21,22 closest to the blown fuse indicator in axial direction are spaced as much as possible from the latter by increasing the curvature thereof, i.e. by imparting smaller radii of curvature to these elements than the radii of curvature of the fusible elements 20,21,22 situated relatively remote from the blown fuse indicator or the closed side of cavity 6.

Referring now more particularly to FIG. 5, it will be apparent from that figure that the ends of terminal bars 5 which project away from housing 1 are situated at different levels, the end projecting away to the right being arranged at a lower level than the end projecting away to the left. The upper surface of the end projecting away to the right is arranged flush with the interface 15 between housing 1 and cover 2. To achieve this end, housing 1 is provided with groove-like recesses 26 which receive the outwardly projecting portion of the right terminal bar 5. The outwardly projecting portion of each left terminal bar 5 engages a recess or keyway 27 in cover 2. Consequently each left terminal bar 5 forms a key,keying cover 2. In other words, in the structure shown terminal bars 5 have the additional function of precluding undesired movements of cover 2 relative to housing 1. It will be apparent from FIGS. 4 and 5 that the composite cavity 6,12 formed by housing 1 and cover 2 includes a center region in which the fusible elements 20,21,22 of stampings or blanks A,B,C,D

are positioned and further includes two end regions which are not occupied by any fusible element means. One of these end regions is situated to one side, and the other of these end regions is situated to the other side, of the center region which contains all the fusible elements 20,21,22. This bunching or or concentration of the fusible elements 20,21,22 in a limited region has been found to be necessary or desirable for best results. The region immediately adjacent the blown fuse indicator mechanism tends to be thermally overstressed when the fuse blows by virtue of the electrodynamic blow action of the system, and this region is particularly prone to dielectric breakdown by virtue of the location of the blown fuse indicator mechanism. This is the reason why no fusible elements but only arc-quenching filler is arranged in that region. The region immediately adjacent to plug 14 which does not contain any fusible element means undergoes minimal thermal stresses incident to blowing of the fuse. This region operates as an effective heat sink and heat dissipator when the fuse performs its current-carrying duty, in particular if the surface of cover 2 provided with the plugs 14, i.e. the rear surface of the polyphase fuse structure, physically engages some heat absorbing and heat dissipating structure such as a metal panel. Such a desirable condition can often readily be established.

The bunching or concentration of fusible elements 20,21,22 inside of a region which is bounded on both sides thereof by regions only containing pulverulent arc-quenching filler, but no fusible elements, could be achieved in ways other than by provision of a housing 1 and a cover 2 having complementary cavities 6 and 12 forming a composite cavity 6,12. The cover might be formed by a substantially flat plate and the housing may define a single cavity having substantially the same shape and volume as the composite cavity 6,12 shown in FIGS. 4 and 5. The structure shown in FIGS. 4 and 5 is, however, particularly desirable when it is intended to dispense with insulating spacers between terminal bars 5, i.e. to use housing 1 as an assembly jig by first inserting terminal bars 5 into housing 1, thereafter sliding stampings or blanks A,B,C,D into grooves 9 of terminal bars 5 located inside of housing 1 and affixed to housing 1, and finally soldering stampings or blanks A,B,C,D inside of housing I to terminal bars 5. This kind of assembling the fuse structure is greatly facilitated if the ends of grooves 9 into which stampings or blanks A,B,C,D are to be inserted are readily accessible by positioning these ends right at the opening of cavity 6. To achieve this end and to provide a body of arctquenching filler 10 intended as heat sink or heat dissipator and not embedding any fusible element or elements calls for a cover 2 having a cavity 12 forming a complement of cavity 6 of housing 1.

While it is desirable to use casing l as an assembly jig as set forth above, it is also possible to space bars 5 by means of a temporary spacer, then slide the stampings A,B,C,D into the grooves of terminal bars 5, and solder stampings A,B,C,D to terminal bars 5, then slide terminal bars 5 and stampings A,B,C,D jointly into housing 1 and finally remove the temporary spacer from the bench assembly unit 5,A,B,C,D.

The number of grooves 9 is preferably an even number in which case equal numbers of grooves 9 and equal numbers of stampings A,B,C,D are arranged on opposite sides of the median plane M of each pair of terminal strips 6, as clearly shown in FIG. 6. As also clearly shown in FIG. 6, the constituent fusible elements 20,21,22 of stampings A and B positioned at one side of median plane M are bent away from median plane M in the direction of said one side, i.e. to the right, as seen in FIG. 6. The constituent fusible elements 20,21,22 of stampings C and D positioned at the side of median plane M opposite said one side thereof are bent away from median plane M in the direction of the side opposite to said one side, i.e. to the left, as seen in FIG. 6. The fusible elements 20,21,22 by which terminal strips 19 are conductively interconnected have a predetermined width W indicated in the bottom region of FIG. 8. Fusible elements 20,21,22 define intermediate gaps having a width which is a multiple of width W. Stampings A,B,C,D are displaced in a direction longitudinally of grooves 9, or in a direction longitudinally of terminal bars 5, a distance equal to the width W of fusible elements 20,21,22. Thus, as shown in FIG. 7 as well as in FIG. 8, stamping C is displaced one step W to the right of stamping A, stamping B is displaced one step W to the right of stamping C, and stamping D is displaced one step W to the right of stamping B. Thus stamping B is displaced two steps 2W to the right of stamping A, and stamping D is displaced two steps W to the right of stamping C. This provides sufficient spacing between fusible elements 20,21,22 of different stampings in a direction longitudinally of grooves 9.

The structure shown in the various figures of the drawings might be conceived as having various sizes, or dimensions. The present polyphase fuse is primarily intended for backup protection of a new generation of miniaturized molded case circuit breakers. Therefore the structure must be smaller than conventional comparable polyphase fuses for back-up protection of molded case circuit breakers, i.e. have dimensions compatible with the dimensions of the aforementioned new generation of miniaturized molded case circuit breakers. This means that the spacing S between the juxtaposed surfaces of terminal bars 5 must be reduced to a smaller distance than found in comparable prior art fuse structures and yet the fuse structure must operate satisfactorily in three-phase circuits wherein the voltage between phases is 600 volt. The most onerous condition is when the fuse structure must also be capable of carrying relatively high load currents. The various figures of the drawings show a structure designed to carry relatively high load currents, e.g. amps. Given the space limitations and consequent dielectric constraints to which the structure is subject, the maximum number of grooves 9 that can be provided in terminal bars is four. In other words, the number of grooves 9 is critical in the sense that it cannot be increased, though it can be readily decreased, e.g. to two, or to one. Considering the prevailing constraints set forth above, in particular in regard to the magnitude of the spacing S and in regard to the voltage rating of 600 volt, there appears to be a critical number for fusible elements 20,21,22 and 3W appears to be a critical number for the widthof the gaps formed between fusible elements 20,21 and fusible elements 21,22, respectively.

It will be apparent from FIG. 6 that the constituent fusible elements 20,21,22 of all four stampings A,B,C,D have a common axis of curvature situated in the median plane M of terminal bars 5 and designated in FIG. 6 by the reference character X. The bell-shaped projection 23 which forms a blown fuse indicator housing is arranged in substantially coaxial relation to axis X, i.e. the axis X forms the axis of projection 23 which is a solid or revolution. This spatial relation is clearly apparent from FIGS. 4 and 5. It makes it possible to maximize the spacing between blown fuse indicator housing 23 and the two fusible elements which are positioned next to it, i.e. fusible elements A 20 and C 20.

While it is desirable for best results and in the interest of minimizing the cost of material and of assembly to dispense with any spacing means for terminal bars 5 in addition to housing 1, i.e. to exclude from cavity 6 any insulating spacer for terminal bars 5, the array of fusible current-carrying means A 20-A 22; B 20 B 22; C 20 C 22 and D 20-D 22 would be effective and desirable in any polyphase fuse irrespective of whether or not such fuse includes insulating spacers arranged in the cavity 6 for spacing terminal bars 5 from each other.

It is apparent from FIG. 8 that the outer edges of terminal strips 19 are parallel. In contrast, the grooves 9 in terminal bars 5 are converging, as are the terminal bars 5 proper. This difference in configuration results in the bending of flat stampings A,B,C,D of FIG. 8 as shown in FIG. 6 when the stampings are pushed in the proper sequence A,B,C,D into grooves 9 of terminal bars 5. Thus the proper bending of fusible elements 21,22,23 does not require any special effort or attention.

We claim as our invention:

1. An electric low-voltage fuse including a. a housing of synthetic resin defining an elongated cavity substantially closed on one side of said housing and open at the opposite side thereof;

b. a pair of terminal bars arranged inside of and located at opposite sides of said cavity and having ends projecting away from said housing, said pair of terminal bars being arranged in abutting relation to opposite walls of said housing bounding said cavity and affixed to said opposite walls, said housing being the only means spacing said pair of terminal bars so that any additional insulating spacing means for said pair of terminal bars engaging said pair of terminal bars is excluded from said cavity, said pair of terminal bars having a plurality of grooves in the juxtaposed surfaces thereof exeach further including a plurality of terminal-stripinterconnecting fusible elements in ribbon form, each of said plurality of fusible elements having a predetermined length exceeding the spacing between said pair of terminal bars, said plurality of stampings being inserted with said pair of terminal strips thereof into said plurality of grooves of said pair of terminal bars and conductively connected to said pair of terminal bars, the constituent fusible elements of said plurality of stampings being arranged substantially out of registry as seen in a direction transversely to said pair of terminal bars, having convex shapes and being bent away from the median plane of said pair of terminal bars, and fusible elements contiguous in a direction longitudinally of said pair of terminal bars being bent alternately in opposite directions.

2. An electric low-voltage fuse as specified in claim 1 wherein said pair of terminal bars is arranged to converge slightly from the open side toward the closed side of said cavity, wherein said plurality of stampings have fusible elements of equal length, and wherein the radii of curvature of said fusible elements decrease progressively from the open side toward the closed side of said cavity.

3. An electric low-voltage fuse as specified in claim 1 wherein the constituent stampings of said plurality of stampings are substantially identical and wherein each of said plurality of stampings is displaced relative to any other of said plurality of stampings in a direction longitudinally of said pair of terminal bars.

4. An electric low-voltage fuse as specified in claim 1 wherein the side wall of said housing substantially closing said cavity has a substantially bell-shaped hollow projection extending into said cavity and housing a blown fuse indicator, and wherein said fusible elements immediately adjacent said hollow projection are bent away from said hollow projection to establish a relatively large spacing between said fusible elements immediately adjacent said hollow projection and said hollow projection.

5. An electric low-voltage fuse as specified in claim 1 wherein the end of one of said pair of terminal bars projecting away from said housing is arranged flush with an interface formed between said housing and said cover,-

wherein said cover defines a keyway and wherein the end of the other of said pair of terminal bars projecting away from said housing is arranged to project above said interface and into said keyway and thus operates as a key positioning said cover relative to said housing.

6. An electric low-voltage fuse as specified in claim 1 including an adhesive bond affixing said cover to said housing and sealing said cavity, said cover being provided with a plugged aperture allowing said arcquenching filler to be filled into said cavity in the presence of said adhesive bond.

7. An electric low-voltage fuse as specified in claim 7 wherein said adhesive bond is formed by cured silicone rubber.

8. An electric low-voltage fuse including a. a housing of synthetic resin defining an elongated cavity substantially closed on one side of said housing and open on the other side thereof;

b. a pair of terminal bars arranged inside of and located at opposite sides of said housing and affixed to said housing and having ends projecting away from said housing, said pair of terminal bars being provided with a plurality of grooves in the juxtaposed surfaces thereof extending in a direction longitudinally of said pair of terminal bars;

c. a pulverulent arc-quenching filler inside of said cavity;

d. a cover of insulating material attached to said housing and closing the open side of said cavity; and

e. a plurality of stampings of a current-limiting metal each including a pair of spaced terminal strips and each further including a plurality of terminal-stripconnecting fusible elements in ribbon form, said fusible elements having a predetermined length exceeding the spacing between said pair of terminal bars, said plurality of stampings being inserted with said pair of terminal strips thereof into said plurality of grooves of said pair of terminal bars and conductively connected to said pair of terminal bars, the constituent fusible elements of said plurality of stampings being arranged substantially out of registry as seen in a direction transversely to said pair of terminal bars, having convex shapes and being bent away from the median plane of said pair of terminal bars, and fusible elements contiguous in a direction longitudinally of said pair of terminal bars being bent alternately in opposite directions.

9. An electric low-voltage fuse as specified in claim 8 wherein the spacing of said pair of terminal bars decreases from the open side of said cavity toward the closed side thereof, wherein the length of said fusible elements of said plurality of stampings is equal, and wherein the curvature of said fusible elements increases progressively as said spacing of said pair of terminal bars decreases.

10. An electric low-voltage fuse as specified in claim 8 wherein the constituent stampings of said plurality of stampings are substantially identical and displaced relative to one another in a direction longitudinally of said pair of terminal bars.

1 1. An electric low-voltage fuse as specified in claim 8 wherein a blown fuse indicator is arranged adjacent said closed side of said housing inside of an indicator housing integral with said housing and wherein said fusible elements immediately adjacent said indicator housing are bent away from said indicator housing to establish a relatively large spacing between said fusible elements immediately adjacent said indicator housing and said indicator housing.

12. An electric low-voltage fuse as specified in claim 8 wherein the end of one of said pair of terminal bars projecting away from said housing is arranged flush with an interface formed between said housing and said 11 cover, wherein said cover defines a keyway and wherein the end of the other of said pair of terminal bars projecting away from said housing is arranged to project above said interface and into said keyway and thus operates as a key positioning said cover relative to said housing.

13. An electric low-voltage fuse as specified in claim 8 including a layer of cured silicone rubber affixing said cover to said housing and providing a gas-tight seal for said cavity, said cover having a plugged aperture allowing filling of said arc-quenching filler into said cavity with said layer of cured silicone rubber in place.

14. An electric low-voltage fuse as specified in claim 8 wherein a. juxtaposed surfaces of said pair of terminal bars are provided with an even number of grooves arranged in equal numbers on opposite sides of the median plane of said pair of terminal bars; and wherein b. the constituent fusible elements of said plurality of stampings positioned at one side of said median plane are bent away from said median plane in the direction of said one side and the constituent fusible elements of said plurality of stampings positioned at the side of said median plane opposite said one side thereof are bent away from said median plane in the direction of said side opposite to said one side.

15. An electric low-voltage fuse as specified in claim 14 wherein said terminal-strip-interconnecting fusible elements of said plurality of stampings have a predetermined width and define intermediate gaps having a width being a multiple of said predetermined width, and wherein said plurality of stampings have a displacement in a direction longitudinally of said pair of terminal strips equal to said predetermined width.

16. An electric low-voltage fuse as specified in claim 15 wherein a. juxtaposed surfaces of said pair of terminal bars are provided with four grooves arranged in pairs on opposite sides of the median plane of said pair of terminal bars; wherein b. the constituent fusible elements of two of said plurality of stampings positioned at one side of said median plane are bent away from said median plane in the direction of said one side, and the constituent fusible elements of two of said plurality of stampings positioned at the side of said median plane opposite said one side thereof are bent away from said median plane in the direction of said side opposite said one side; and wherein c. each of said plurality of stampings includes three said terminal-strip-interconnecting fusible elements in ribbon form having a predetermined width and defining intermediate gaps having a width three times said intermediate width.

17. An electric low-voltage fuse including a. a housing of electric insulating material defining an elongated cavity closed on one side of said housing and open at the opposite side thereof;

b. a cover of electric insulating material for said housing, said cover defining an elongated cavity closed on one side of said cover and open at the opposite side thereof, said cover and said housing bejn arranged to abut at the sides thereof where said ousmg cavity and said cover cavity are open and said housing cavity and said cover cavity jointly forming a composite cavity;

c. a pulverulent arc-quenching filler inside of said composite cavity;

d. a pair of terminal bars projecting from the outside of said housing into the inside thereof and engaging juxtaposed walls of said housing bounding said housing cavity, each of said pair of terminal bars having a plurality of grooves on juxtaposed surfaces thereof extending in a direction longitudinally of said housing cavity; and

e. an array of fusible current-carrying means confined to the center region of said composite cavity and leaving a first region adjacent the closed side of said housing cavity and a second region adjacent said closed side of said cover cavity where said pulverulent arc-quenching filler is substantially free from any fusible current-carrying means, said array of fusible current-carrying means being formed by a plurality of stampings of a currentlimiting metal each including a pair of spaced terminal strips and each further including a plurality of terminal-strip-interconnecting fusible elements in ribbon form, each of said plurality of fusible elements having a predetermined length exceeding the spacing between said pair of terminal bars, said plurality of stampings being inserted with said pair of terminal strips thereof into said plurality of grooves in said pair of terminal bars and conductively connected to said pair of terminal bars, the constituent fusible elements of said plurality of stampings being arranged substantially out or registry as seen in a direction transversely to said pair of terminal bars, having convex shapes and being bent away from the median plane of said pair of terminal bars, and fusible elements contiguous in a direction longitudinally of said pair of terminal bars being bent alternately in opposite directions.

18. An electric low-voltage fuse as specified in claim 17 wherein a. said pair of terminal bars is affixed to said housing and said housing is the only means spacing said pair of terminal bars so that any additional insulating spacing means for said pair of terminal bars is excluded from said cavity;

b. juxtaposed surfaces of said pair of terminal bars are provided with an even number of grooves arranged in equal numbers on opposite sides of the median plane of said pair of terminal bars; and wherein c. the constituent fusible elements of said plurality of stampings positioned at one side of said median plane are bent away from said median plane in the direction of said one side, and the constituent fusible elements of said plurality of stampings positioned at the side of said median plane opposite said one side thereof are bent away from said median plane in the direction of said side opposite to said one side.

* III 

1. An electric low-voltage fuse including a. a housing of synthetic resin defining an elongated cavity substantially closed on one side of said housing and open at the opposite side thereof; b. a pair of terminal bars arranged inside of and located at opposite sides of said cavity and having ends projecting away from said housing, said pair of terminal bars being arranged in abutting relation to opposite walls of said housing bounding said cavity and affixed to said opposite walls, said housing being the only means spacing said pair of terminal bars so that any additional insulating spacing means for said pair of terminal bars engaging said pair of terminal bars is excluded from said cavity, said pair of terminal bars having a plurality of grooves in the juxtaposed surfaces thereof extending in a direction longitudinally of said pair of terminal bars; c. a pulverulent arc-quenching filler inside said cavity; d. a cover of insulating material attached to said housing and closing the open side of said cavity; and e. a plurality of stampings of a current-limiting metal each including a pair of spaced terminal strips and each further including a plurality of terminal-strip-interconnecting fusible elements in ribbon form, each of said plurality of fusible elements having a predetermined length exceeding the spacing between said pair of terminal bars, said plurality of stampings being inserted with said pair of terminal strips thereof into said plurality of grooves of said pair of terminal bars and conductively connected to said pair of terminal bars, the constituent fusible elements of said plurality of stampings being arranged substantially out of registry as seen in a direction transversely to said pair of terminal bars, having convex shapes and being bent away from the median plane of said pair of terminal bars, and fusible elements contiguous in a direction longitudinally of said pair of terminal bars being bent alternately in opposite directions.
 2. An electric low-voltage fuse as specified in claim 1 wherein said pair of terminal bars is arranged to converge slightly from the open side toward the closed side of said cavity, wherein said plurality of stampings have fusible elements of equal length, and wherein the radii of curvature of said fusible elements decrease progressively from the open side toward the closed side of said cavity.
 3. An electric low-voltage fuse as specified in claim 1 wherein the constituent stampings of said plurality of stampings are substantially identical and wherein each of said plurality of stampings is displaced relative to any other of said plurality of stampings in a direction longitudinally of said pair of terminal bars.
 4. An electric low-voltage fuse as specified in claim 1 wherein the side wall of said housing substantially closing said cavity has a substantially bell-shaped hollow projection extending into said cavity and housing a blown fuse indicator, and wherein said fusible elements immediately adjacent said hollow projection are bent away from said hollow projection to establish a relatively large spacing between said fusible elements immediately adjacent said hollow projection and said hollow projection.
 5. An electric low-voltage fuse as specified in claim 1 wherein the end of one of said pair of terminal bars projecting away from said housing is arranged flush with an interface formed between said housing and said cover, wherein said cover defines a keyway and wherein the end of the other of said pair of terminal bars projecting away from said housing is arranged to project above said interface and into said keyway and thus operates as a key positioning said cover relative to said housing.
 6. An electric low-voltage fuse as specified in claim 1 including an adhesive bond affixing said cover to said housing and sealing said cavity, said cover being provided with a plugged aperture allowing said arc-quenching filler to be filled into said cavity in the presence of said adhesive bond.
 7. An electric low-voltage fuse as specified in claim 7 wherein said adhesive bond is formed by cured silicone rubber.
 8. An electric low-voltage fuse including a. a housing of synthetic resin defining an elongated cavity substantially closed on one side of said housing and open on the other side thereof; b. a pair of terminal bars arranged inside of and located at opposite sides of said housing and affixed to said housing and having ends projecting away from said housing, said pair of terminal bars being provided with a plurality of grooves in the juxtaposed surfaces thereof extending in a direction longitudinally of said pair of terminal bars; c. a pulverulent arc-quenching filler inside of said cavity; d. a cover of insulating material attached to said housing and closing the open side of said cavity; and e. a plurality of stampings of a current-limiting metal each including a pair of spaced terminal strips and each further including a plurality of terminal-strip-connecting fusible elements in ribbon form, said fusible elements having a predetermined length exceeding the spacing between said pair of terminal bars, said plurality of stampings being inserted with said pair of terminal strips thereof into said plurality of grooves of said pair of terminal bars and conductively connected to said pair of terminal bars, the constituent fusible elements of said plurality of stampings being arranged substantially out of registry as seen in a direction transversely to said pair of terminal bars, having convex shapes and being bent away from the median plane of said pair of terminal bars, and fusible elements contiguous in a direction longitudinally of said pair of terminal bars being bent alternately in opposite directions.
 9. An electric low-voltage fuse as specified in claim 8 wherein the spacing of said pair of terminal bars decreases from the open side of said cavity toward the closed side thereof, wherein the length of said fusible elements of said plurality of stampings is equal, and wherein the curvature of said fusible elements increases progressively as said spacing of said pair of terminal bars decreases.
 10. An electric low-voltage fuse as specified in claim 8 wherein the constituent stampings of said plurality of stampings are substantially identical and displaced relative to one another in a direction longitudinally of said pair of terminal bars.
 11. An electric low-voltage fuse as specified in claim 8 wherein a blown fuse indicator is arranged adjacent said closed side of said housing inside of an indicator housing integral with said housing and wherein said fusible elements immediately adjacent said indicator housing are bent away from said indicator housing to establish a relatively large spacing between said fusible elements immediately adjacent said indicator housing and said indicator housing.
 12. An electric low-voltage fuse as specified in claim 8 wherein the end of one of said pair of terminal bars projecting away from said housing is arranged flush with an interface formed between said housing and said cover, wherein said cover defines a keyway and wherein the end of the other of said pair of terminal bars projecting away from said housing is arranged to project above said interface and into said keyway and thus operates as a key positioning said cover relative to said housing.
 13. An electric low-voltage fuse as specified in claim 8 including a layer of cured silicoNe rubber affixing said cover to said housing and providing a gas-tight seal for said cavity, said cover having a plugged aperture allowing filling of said arc-quenching filler into said cavity with said layer of cured silicone rubber in place.
 14. An electric low-voltage fuse as specified in claim 8 wherein a. juxtaposed surfaces of said pair of terminal bars are provided with an even number of grooves arranged in equal numbers on opposite sides of the median plane of said pair of terminal bars; and wherein b. the constituent fusible elements of said plurality of stampings positioned at one side of said median plane are bent away from said median plane in the direction of said one side and the constituent fusible elements of said plurality of stampings positioned at the side of said median plane opposite said one side thereof are bent away from said median plane in the direction of said side opposite to said one side.
 15. An electric low-voltage fuse as specified in claim 14 wherein said terminal-strip-interconnecting fusible elements of said plurality of stampings have a predetermined width and define intermediate gaps having a width being a multiple of said predetermined width, and wherein said plurality of stampings have a displacement in a direction longitudinally of said pair of terminal strips equal to said predetermined width.
 16. An electric low-voltage fuse as specified in claim 15 wherein a. juxtaposed surfaces of said pair of terminal bars are provided with four grooves arranged in pairs on opposite sides of the median plane of said pair of terminal bars; wherein b. the constituent fusible elements of two of said plurality of stampings positioned at one side of said median plane are bent away from said median plane in the direction of said one side, and the constituent fusible elements of two of said plurality of stampings positioned at the side of said median plane opposite said one side thereof are bent away from said median plane in the direction of said side opposite said one side; and wherein c. each of said plurality of stampings includes three said terminal-strip-interconnecting fusible elements in ribbon form having a predetermined width and defining intermediate gaps having a width three times said intermediate width.
 17. An electric low-voltage fuse including a. a housing of electric insulating material defining an elongated cavity closed on one side of said housing and open at the opposite side thereof; b. a cover of electric insulating material for said housing, said cover defining an elongated cavity closed on one side of said cover and open at the opposite side thereof, said cover and said housing being arranged to abut at the sides thereof where said housing cavity and said cover cavity are open and said housing cavity and said cover cavity jointly forming a composite cavity; c. a pulverulent arc-quenching filler inside of said composite cavity; d. a pair of terminal bars projecting from the outside of said housing into the inside thereof and engaging juxtaposed walls of said housing bounding said housing cavity, each of said pair of terminal bars having a plurality of grooves on juxtaposed surfaces thereof extending in a direction longitudinally of said housing cavity; and e. an array of fusible current-carrying means confined to the center region of said composite cavity and leaving a first region adjacent the closed side of said housing cavity and a second region adjacent said closed side of said cover cavity where said pulverulent arc-quenching filler is substantially free from any fusible current-carrying means, said array of fusible current-carrying means being formed by a plurality of stampings of a current-limiting metal each including a pair of spaced terminal strips and each further including a plurality of terminal-strip-interconnecting fusible elements in ribbon form, each of said plurality of fusible elements having a predetermined length exceeding the spacing between said pair of Terminal bars, said plurality of stampings being inserted with said pair of terminal strips thereof into said plurality of grooves in said pair of terminal bars and conductively connected to said pair of terminal bars, the constituent fusible elements of said plurality of stampings being arranged substantially out or registry as seen in a direction transversely to said pair of terminal bars, having convex shapes and being bent away from the median plane of said pair of terminal bars, and fusible elements contiguous in a direction longitudinally of said pair of terminal bars being bent alternately in opposite directions.
 18. An electric low-voltage fuse as specified in claim 17 wherein a. said pair of terminal bars is affixed to said housing and said housing is the only means spacing said pair of terminal bars so that any additional insulating spacing means for said pair of terminal bars is excluded from said cavity; b. juxtaposed surfaces of said pair of terminal bars are provided with an even number of grooves arranged in equal numbers on opposite sides of the median plane of said pair of terminal bars; and wherein c. the constituent fusible elements of said plurality of stampings positioned at one side of said median plane are bent away from said median plane in the direction of said one side, and the constituent fusible elements of said plurality of stampings positioned at the side of said median plane opposite said one side thereof are bent away from said median plane in the direction of said side opposite to said one side. 